Heat exchanger comprising microstructure elements and separation unit comprising such a heat exchanger

ABSTRACT

The invention relates to a heat exchanger comprising parallel plates and spacers arranged in parallel and defining i) rough primary channels and ii) secondary channels arranged so as to exchange heat. Said heat exchanger comprises a primary liquid inlet to be fluidically connected to a primary liquid dispenser. Each rough primary channel has the shape of a prism having a polygonal cross-section and consisting of a plurality of essentially flat faces. The primary channels comprise rough primary channels. Each rough primary channel has microstructure elements which are distributed along the entire length of the channel and have dimensions of between 1 μm and 300 μm.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a § 371 of International PCT Application PCT/FR2016/050851 filed Apr. 13, 2016, which claims the benefit of FR1553397, filed Apr. 16, 2015, both of which are herein incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to an exchange of heat between a primary liquid, for example containing oxygen, and a secondary fluid, for example containing nitrogen. Furthermore, the present invention relates to a cryogenic gas separation unit comprising such an exchange of heat.

The present invention relates to the field of heat exchangers configured to produce exchanges of heat between a primary liquid and a secondary fluid. In particular, the present invention can be applied to the field of cryogenic gas separation, in particular the separation of air gases, acid gases and natural gas.

BACKGROUND

EP0130122A1 describes a heat exchanger which generally comprises parallel plates, parallel spacers, which define i) primary channels and ii) secondary channels, and an inlet linked to a bath of primary liquid via a distributor. In general, each primary channel has an overall prism form with rectangular base, the primary liquid circulating along the prism and at right angles to the rectangular base.

When the heat exchanger of EP0130122A1 is in service, the primary liquid which circulates in the primary channels exchanges heat with the secondary fluid which flows in the secondary channels. In the case of a cryogenic air separation unit, the primary liquid contains a large proportion of oxygen and the secondary fluid contains a large proportion of gaseous nitrogen. The primary liquid flow rate is relatively low in a primary channel.

However as FIG. 1 shows in the present application, the primary channels of EP0130122A1 have small transverse dimensions, in this case millimetric, such that primary liquid is not distributed uniformly over all the rectangular perimeter 51 of each smooth primary channel 50. Therefore, the primary liquid forms menisci 52 and is concentrated in the corners 53 of the rectangular perimeter 51 of each smooth primary channel 50, which induces the occurrence of dry zones on the long sides 54 of the rectangular perimeter 51 of each smooth primary channel 50.

The number and the surface area of the dry zones increase as the primary liquid flowing toward the outlets of the smooth primary channels vaporizes. These dry zones are therefore not used in exchanges of heat, which reduces the efficiency of the heat exchanger. Furthermore, these dry zones risk causing deposits of impurities, which can ultimately cause a failing in the safety of personnel and of the equipment.

SUMMARY OF THE INVENTION

The aim of the present invention is in particular to wholly or partly resolve the abovementioned problems, by providing a heat exchanger that makes it possible to conserve primary and secondary channels with a conventional geometry, without generating additional head losses, while increasing the thermal transfer and the safety of the heat exchanger.

To this end, the subject of the invention is a heat exchanger, for producing exchanges of heat between a primary liquid and a secondary fluid, the heat exchanger comprising at least:

-   -   several plates disposed parallel to one another,     -   spacers extending between the plates and disposed parallel to         one another so as to define i) primary channels conformed for         the flow of the primary liquid and ii) secondary channels         conformed for the flow of the secondary fluid, each primary         channel being arranged so as to be able to exchange heat with at         least one respective secondary channel,     -   a primary liquid inlet, intended to be linked fluidically to a         primary liquid distributor,

the heat exchanger being characterized in that each primary channel has an overall prism form with polygonal section, the prism being made up of several overall flat faces, and

in that the primary channels comprise rough primary channels, each rough primary channel having microstructure elements having dimensions of between 1 μm and 300 μm, preferably between 1 μm and 100 μm, and

in that the microstructure elements are configured such that, for each rough primary channel:

r>1+1.3·10³ ·R _(a)·ε

in which:

-   -   r is the ratio of the real surface of a respective rough primary         channel, as numerator, to the geometrical surface of a         respective rough primary channel, as denominator,     -   R_(a) (in m) is the arithmetic mean deviation relative to the         median line, and     -   ε is the void fraction of the real surface of a respective rough         primary channel.

The ratio r is sometimes called “roughness coefficient” or “roughness”. The arithmetic mean deviation R_(a) (in m) represents the roughness of the rough primary channel. In the present application, the term “median line” designates a line situated at the mean altitude of the real surface. In practice, the median line can be calculated from the topographic recording of the cross-sectional profile of the surface by applying the least squares method.

In the present application, the term “void fraction of a surface” corresponds to a fraction calculated as follows: a slice is considered whose thickness is equal to the height of the highest peak (relative to the lowest point) of this surface. On this slice, the void fraction c corresponds to the ratio of the volume not occupied by microstructure elements to the total volume of the slice. This ratio is expressed as follows:

$ɛ = \frac{V_{tot} - V_{surf}}{V_{tot}}$

in which:

V_(tot) (in m³) is the volume contained between the highest point and the lowest point of the real surface, and

V_(surf) (in m³) is the volume contained between the real surface and the lowest point of the real surface.

Consequently:

ε=1− z/R _(z)

in which: R_(z) is the height of the highest peak relative to the lowest point of the surface,

z (in m) is the height of a respective point relative to the lowest point of the real surface, the height z being measured point-by-point, z (in m) is the arithmetic mean of the height z measured point-by-point.

Thus, such a heat exchanger makes it possible to conserve primary and secondary channels with a conventional geometry, therefore simple to manufacture and implement, without generating additional head losses, while increasing the thermal transfer and safety when the heat exchanger is in service. In effect, the microstructure elements make it possible to increase the thermal transfer, because the exchange surface area and the wetted surface are greater. Also, the safety of the heat exchanger is enhanced, because of the great wettability of the primary channels, which makes it possible to avoid any dry vaporization of oxygen. Moreover, measurements have shown that the prismatic geometry with polygonal base exhibited heat transfer coefficients higher than a tubular geometry with circular base for example.

The surface treatment, with the microstructure elements, makes it possible to wet all the perimeter of the primary channel and therefore increase the exchange surface.

In most applications, the primary liquid and the secondary fluid are cryogenic fluids. The primary liquid and the secondary fluid introduced into the heat exchanger can be single-phase, that is to say all liquid or all gaseous, or two-phase, that is to say made up of liquid and gas. During their flow in the heat exchanger, the proportions of the phases of the primary liquid and of the secondary fluid can vary.

According to one embodiment of the invention, each polygonal section has dimensions of between 1 mm and 10 mm, preferably between 3 mm and 7 mm, a rectangular polygonal section having, for example, an approximate length equal to 5 mm and an approximate width equal to 1.5 mm.

Thus, such transverse dimensions make it possible to adapt the heat exchanger to the primary liquid and secondary fluid flow rates to be handled.

According to one embodiment of the invention, microstructure elements are distributed substantially over all the internal periphery of each rough primary channel.

Thus, such a distribution guarantees the wetting of all the polygonal section of each rough primary channel.

According to one embodiment of the invention, for each respective rough primary channel, the microstructure elements are distributed over at least 80% of the surface of the rough primary channel.

Thus, each rough primary channel is substantially covered with microstructure elements which increase the exchange surface area.

According to one embodiment of the invention, the microstructure elements have mutually similar dimensions and mutually similar forms, and in which the microstructure elements are configured such that, for each rough primary channel:

r>1+1.3·10³ ·h·ε

in which: h (in m) is the mean height of the microstructure elements.

Thus, such similar microstructure elements make it possible to obtain a greater wettability of each rough primary channel and to control the minimum thickness of the primary liquid film.

For example, similar dimensions of the microstructure elements can exhibit a deviation of 20% from one microstructure element to another. Two microstructure elements having similar forms have all their dimensions similar.

In the present application, the term “real surface” designates in particular the surface obtained after manufacture and the term “geometrical surface” designates in particular a perfect surface, therefore a smooth surface, apart from any microstructure elements present; a geometrical surface can be fully defined geometrically by nominal dimensions. The geometrical surface is sometimes called “projected surface” when it is considered in a plane.

In the present application, the term “surface” can designate either a topological entity or the surface area of this topological entity.

According to one embodiment of the invention, the microstructure elements are distributed uniformly. In particular, the microstructure elements can be similar and distributed uniformly.

Thus, such a uniform distribution makes it possible to guarantee a greater wettability of each rough primary channel and to control the minimum thickness of the primary liquid film.

Alternatively to the preceding embodiment, the microstructure elements can be similar and distributed non-uniformly, for example randomly.

According to one embodiment of the invention, the microstructure elements are configured such that, for each rough primary channel:

$d < \sqrt{\frac{7.5 \cdot 10^{- 4} \cdot P}{ɛ}}$

in which:

-   -   d (in m) is the mean distance between the centers of the         adjacent microstructure elements, the centers being situated on         the geometrical surface of the rough primary channel,     -   P (in m) is the mean perimeter of the section of the         microstructure elements.

According to one embodiment of the invention, the microstructure elements are configured such that, for each rough primary channel:

$\frac{r - 1 - {1.3 \cdot 10^{3} \cdot h \cdot ɛ}}{{ɛ/h} + {6.7 \cdot {10^{- 6}/d^{2}}}} > {4.2 \cdot 10^{- 8}}$

and in which the microstructure elements (30) are also configured such that, for each rough primary channel (21):

$d > \sqrt{\frac{S}{0.4}}$

in which: S (in m²) is the mean surface of the section of the microstructures.

Microstructure elements thus configured make it possible to have a rate of propagation of the liquid matched to the heat exchange method.

According to one embodiment of the invention, the microstructure elements have irregular forms, for example with irregular dimensions, the microstructure elements also being able to be distributed non-uniformly, for example randomly.

In other words, the intervals between two neighboring microstructure elements are variable, therefore not constant, over all the real surface of the rough primary channel considered.

Thus, such a non-uniform distribution makes it possible to obtain a constant wettability all along each rough primary channel, by limiting the surface area of each zone without microstructure elements.

Alternatively to this variant, each microstructure element can have a regular form or geometry, for example in overall cylinder, prism, cone or similar form. In this variant, the microstructure elements of regular forms are configured such that, for each rough primary channel:

r>1+1.3·10³ ·h·ε

But, in a variant in which the microstructure elements have irregular forms, the microstructure elements are configured such that:

r>1+1.3·10³ ·R _(a)ε

According to one embodiment of the invention, the microstructure elements are configured such that, for each rough primary channel:

$\frac{r - 1 - {1.3 \cdot 10^{3} \cdot R_{a} \cdot ɛ}}{{ɛ/R_{a}} + {1.2 \cdot 10^{5}}} > {4.2 \cdot {10^{- 8}.}}$

Such microstructure elements form a roughness which increases in particular the wettability of the surface of each rough primary channel, which allows the liquid to wet all the surface of the rough primary channel even in the presence of a recess.

According to one embodiment of the invention, each rough primary channel out of at least a part of the rough primary channels has an overall prism form with rectangular base.

As the adjective “overall” indicates, the prism can have an approximately rectangular base. For example, the edges of the rectangle defining the base of the prism can be rounded, for example by braze.

Thus, such a form of rough primary channel, with rectangular base, makes it possible to conserve rough primary channels and secondary channels with a conventional geometry, therefore simple to manufacture and to implement in the assembly of the heat exchanger.

According to one embodiment of the invention, the microstructure elements are distributed only on the long sides of the rectangular base.

In other words, the short sides of the rectangular perimeter have no microstructure elements. In effect, the short sides can be wetted because of the natural formation of the menisci in the corners of the rectangular perimeter.

According to one embodiment of the invention, the microstructure elements are distributed so as to define between them passages for the flow of the primary liquid.

In other words, the microstructure elements extend overall above the level of the geometrical surface.

Thus, the microstructure elements are distributed so as to define a surface condition with an open roughness, that is to say a roughness defined by peaks or locks but without narrow cavities. A cavity is considered narrow when the peaks which surround it are too close together to allow a circulation of the liquid.

According to one embodiment of the invention, each rough primary channel has an arithmetic roughness R_(a) of between 1 μm and 60 μm.

Thus, such an arithmetic roughness makes it possible to obtain a great wettability of the rough primary channels.

According to one embodiment of the invention, each rough primary channel has nanostructure elements distributed over at least 80% of its length, each nanostructure element having dimensions of between 1 nm and 500 nm.

Thus, such nanostructure elements make it possible to maximize the wettability of each rough primary channel.

According to a variant of the invention, the nanostructure elements are distributed over the surface of each rough primary channel. Alternatively or in addition to this variant of the invention, the nanostructure elements can be distributed over the surfaces of the microstructure elements.

According to a variant of the invention, the coating is made up of a metal material and/or of an inorganic material, for example of a ceramic material. The coating can be obtained by spray deposition (sometimes referred to as “spray”) of particles and/or of fibers on the surface of each rough primary channel.

According to one embodiment of the invention, the microstructure elements are formed by a treatment of the surface of each primary element, for example by anodization, by sandblasting, by shotblasting or by chemical etching or even by powder sintering, by molten metal spraying, by laser, by photolithography or by mechanical etching of rolling, brushing or printing type.

Furthermore, the microstructure elements can be formed by a coating obtained by impregnation, by spray deposition by plasma deposition, by an additive manufacturing process, for example by three-dimensional printing.

According to a variant of the invention, the plates and/or the spacers are composed of materials selected from the group consisting of aluminum, copper, nickel, chrome, iron and alloys of aluminum, an alloy of copper, of nickel, of chrome, of iron, for example a nickel-chrome alloy or a nickel-chrome-iron alloy.

Thus, such plates and/or spacers make it possible to handle standard primary liquids and secondary fluids in the field of cryogenics, for example a liquid containing oxygen and a gas containing nitrogen for separating the air gases, the acid gases and natural gas.

According to one embodiment of the invention, the heat exchanger is configured to form a vaporizer-condenser, the lengths of the rough primary channels and the lengths of the secondary channels being determined such that the exchanges of heat make it possible to totally or partially vaporize the primary liquid and to totally or partially condense the secondary fluid introduced in secondary gas form.

Thus, such a vaporizer-condenser makes it possible to handle the standard primary liquids and secondary fluids in the field of cryogenics, for example a liquid containing oxygen and a gas containing nitrogen for separating the components of air.

According to one embodiment of the invention, said primary liquid inlet is placed at an altitude greater than the rough primary channels when the heat exchanger is in service such that the primary liquid distributor introduces the primary liquid in the form of a film flowing by gravity through said at least one primary liquid inlet into the rough primary channels.

According to a variant of the invention, the secondary channels comprise rough secondary channels, each rough secondary channel being formed in a way similar to the rough primary channels. In particular, a rough secondary channel can have microstructure elements which have dimensions of between 1 μm and 300 μm, preferably between 1 μm and 100 μm, and which satisfy the equations applicable to the rough primary channels. More generally, each of the features mentioned above for the rough primary channels can be applied to the rough secondary channels. However, these features are not repeated here, so as to simplify the reading of the present patent application.

Moreover, the subject of the present invention is a separation unit, for separating gas by cryogenics, the separation unit comprising at least one vaporizer-condenser-forming heat exchanger according to the invention, the vaporizer-condenser being configured to allow an exchange of heat between a liquid containing oxygen and a gas containing nitrogen.

Thus, such a cryogenic gas separation unit makes it possible to handle the standard primary liquids and secondary fluids in the field of cryogenics, for example a liquid containing oxygen and a gas containing nitrogen for separating the components of air.

The embodiments and the variants mentioned above can be taken in isolation or according to any technically acceptable combination.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be well understood and its advantages will also emerge in light of the following description, given purely as a nonlimiting example and with reference to the attached drawings, in which:

FIG. 1 is a transverse section of a smooth primary channel of the prior art;

FIG. 2 is a perspective schematic view of a separation unit according to the invention and comprising a heat exchanger according to the invention;

FIG. 3 is a transverse section of a rough primary channel according to a first embodiment of the invention;

FIG. 4 is a perspective view illustrating microstructure elements disposed on the rough primary channel of FIG. 1;

FIG. 5 is a perspective view illustrating microstructure elements disposed on a rough primary channel according to a second embodiment of the invention;

FIG. 6 is a cross-sectional schematic view of a pattern forming microstructure elements for the rough primary channel of FIG. 4; and

FIG. 7 is a cross-sectional schematic view of a pattern forming microstructure elements for a rough primary channel according to a third embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2, 3 and 4 illustrate a heat exchanger 1 for producing exchanges of heat between a primary liquid and a secondary fluid. The heat exchanger 1 belongs to a separation unit 2 for separating the components of air by cryogenics.

In the example of FIGS. 2 to 4, the heat exchanger 1 is configured to form a vaporizer-condenser configured to allow an exchange of heat between a liquid containing oxygen and a gas containing nitrogen. The plate heat exchanger 1 can thus be used to vaporize an oxygen-rich liquid by exchange of heat with a nitrogen-rich gas which is concomitantly condensed.

The heat exchanger 1 comprises several plates 11, which are disposed parallel to one another, and spacers 12, which extend between the plates 11 and which are also disposed parallel to one another. In the example of FIGS. 2 to 4, the plates 11 and the spacers 12 are made of an aluminum alloy. The plates 11 are brazed together in a manner that is known per se.

The spacers 12 are disposed so as to define:

i) primary channels conformed for the flow of the primary liquid, in this case containing liquid dioxygen (O2L), the primary channels comprising rough primary channels 21; and

ii) secondary channels 22 conformed for the flow of the secondary fluid, in this case containing gaseous dinitrogen (N2G).

Each rough primary channel 21 is arranged so as to be able to exchange heat with two respective secondary channels 22. To this end, the rough primary channels 21 and the secondary channels 22 follow one another alternately in a direction of stacking D of the plates 11. The rough primary channels 21 and the secondary channels 22 are here mounted in a counter-current configuration. Alternatively, the rough primary channels 21 and the secondary channels 22 can be mounted in a co-current configuration.

The heat exchanger 1 also comprises a primary liquid inlet 14 which is linked fluidically to a primary liquid distributor 6 belonging to the separation unit 2. The primary liquid O2L forms a bath above the primary liquid distributor 6.

The inlet 14 is placed at an altitude greater than the rough primary channels 21 when the heat exchanger 1 is in service. The altitude is measured in the usual manner with reference to an upward vertical direction. Thus, the primary liquid distributor 6 introduces the primary liquid in the form of a film flowing by gravity through the inlet 14 into the rough primary channels.

Moreover, each rough primary channel 21 has an overall prism form with polygonal section and extending along a longitudinal direction X. This prism is made up of several overall flat faces. The edges of the rectangle defining the base of the prism are here a little rounded by braze. Each polygonal section—or polygonal perimeter—of the prism here has dimensions of between 1 mm and 5 mm.

As FIG. 3 shows, each rough primary channel 21 here has an overall prism form with rectangular base and extending along the longitudinal direction X. In this case, the rectangular section has an approximate height H21 equal to 4.5 mm and an approximate width W21 equal to 1.5 mm. When the heat exchanger 1 is in service, the primary liquid flows along the prism and at right angles to the rectangular base.

Furthermore, as FIG. 3 shows, each rough primary channel 21 has microstructure elements 30. The microstructure elements 30 are distributed or allocated over at least 80% of the length L21 of the rough primary channel 21 considered. To dimension the separation unit 2, the lengths L21 of the rough primary channels 21 and the lengths of the secondary channels 22 are determined such that the exchanges of heat make it possible to vaporize all or part of the primary liquid and condense all or part of the secondary fluid introduced in secondary gas form.

Each microstructure element 30 has dimensions of between 1 μm and 300 μm. Each microstructure element 30 here has the overall form of a narrow cylinder. As FIG. 4 shows, the microstructure elements 30 have mutually similar dimensions and forms. The microstructure elements 30 are configured such that, for each rough primary channel 21:

r>1+1.3·10³ ·R _(a)·ε.

in which:

-   -   r is the ratio of the real surface of a respective rough primary         channel 21, as numerator, to the geometrical surface of a         respective rough primary channel 21, as denominator,     -   R_(a) (in m) is the arithmetic mean deviation relative to the         median line, and     -   ε is the void fraction of the real surface of the respective         rough primary channel 21.

In the example of FIGS. 1 to 4, the microstructure elements 30 are regular and distributed uniformly, and they are configured such that, for each rough primary channel 21:

r>1+1.3·10³ ·h·ε

in which: h (in m) is the mean height of the microstructure elements 30, the mean height being calculated from the heights H30 of each microstructure element 30.

In the example of FIG. 4, the microstructure elements 30 are not distributed over all the rectangular section of each rough primary channel 21. On the contrary, the microstructure elements 30 are distributed only on the long sides 44 of the rectangular section of each rough primary channel 21, but not on the short sides 45. In other words, the short sides 45 have no microstructure elements 30. In effect, the short sides 45 are wetted because of the natural formation of the menisci in the corners of the rectangular section.

The microstructure elements 30 are distributed so as to define between them passages for the flow of the primary liquid O2L, which defines a surface condition with an open roughness. Furthermore, the microstructure elements 30 are distributed uniformly. In other words, the interval between two successive microstructure elements 30 is substantially constant in any direction. The microstructure elements 30 are therefore arranged according to a uniform and ordered matrix.

The microstructure elements 30 are here configured such that, for each rough primary channel 21:

r>1+1.3·10³ ·h·ε

in which:

The microstructure elements 30 are here configured such that, for each rough primary channel 21:

$d < \sqrt{\frac{7.5 \cdot 10^{- 4} \cdot P}{ɛ}}$

in which:

-   -   d (in m) is the mean distance between the centers of the         adjacent microstructure elements 30, the centers being situated         on the geometrical surface of the rough primary channel 21, the         mean distance being calculated from each distance d30         separating, two-by-two, the centers of the adjacent         microstructure elements 30,     -   P (in m) is the mean perimeter of the section of the         microstructure elements 30, and

furthermore, the microstructure elements 30 are here configured such that, for each rough primary channel 21:

$\frac{r - 1 - {1.3 \cdot 10^{3} \cdot h \cdot ɛ}}{{ɛ/h} + {6.7 \cdot {10^{- 6}/d^{2}}}} > {4.2 \cdot 10^{- 8}}$

Furthermore, the microstructure elements 30 are configured such that, for each rough primary channel 21:

$d > \sqrt{\frac{S}{0.4}}$

in which: S (in m²) is the mean surface of the section of the microstructures.

Because of the presence of the microstructure elements 30, each rough primary channel 21 has an arithmetic roughness Ra of between 1 μm and 60 μm. The arithmetic roughness Ra is a statistical parameter representing the arithmetic mean deviation relative to the median line of the surface of a rough primary channel 21 considered.

Furthermore, each rough primary channel 21 can have nanostructure elements (not represented) distributed over at least 80% of its length L21. Each nanostructure element has dimensions of between 1 nm and 100 nm. The nanostructure elements can be distributed over the surface of each rough primary channel 21 and over the surfaces of the microstructure elements 30.

Moreover, the microstructure elements 30 form a coating obtained here by spray deposition (sometimes referred to by the term “spray”) of particles on the surface of each rough primary channel 21. The particles forming this coating are here made up of a metal material.

FIGS. 5 and 6 show a part of a rough primary channel 121 belonging to a heat exchanger according to a second embodiment of the invention. Inasmuch as the rough primary channel 121 is similar to the rough primary channel 21, the description of the heat exchanger and of the rough primary channel 21 given hereinabove in relation to FIGS. 1 to 4 can be transposed to the rough primary channel 121 and to its heat exchanger, apart from the notable differences described hereinbelow.

The rough primary channel 121 differs from the rough primary channel 21, essentially in that the microstructure elements 130 have a relatively wide and high cylinder form and in that the interval between two microstructure elements 130 is greater than the interval between two microstructure elements 30.

FIG. 7 illustrates, in section, in a plane x-z, a part of a rough primary channel 221 belonging to a heat exchanger according to a third embodiment of the invention. Inasmuch as the rough primary channel 221 is similar to the rough primary channel 21, the description of the heat exchanger and of the rough primary channel 21 given hereinabove in relation to FIGS. 1 to 4 can be transposed to the rough primary channel 221 and to its heat exchanger, apart from the notable differences described hereinbelow.

The rough primary channel 221 differs from the rough primary channel 21, notably in that the microstructure elements 230 have irregular, therefore mutually dissimilar, forms and dimensions. Furthermore, the rough primary channel 221 differs from the rough primary channel 21, notably in that the microstructure elements 230 are distributed non-uniformly, in this case randomly. In other words, the intervals between two neighboring microstructure elements 230 are variable, therefore not constant, over all the real surface of the rough primary channel 221.

The microstructure elements 230 are configured such that, for each rough primary channel 21:

r>1+1.3·10³ ·R _(a)·ε.

In FIG. 7, a median line z represents the arithmetic mean of the height z measured point-by-point, including, for example, heights z1, z2, z3, z4 et z5. R_(z) is the height of the highest peak relative to the lowest point of the surface.

Obviously, the present invention is not limited to the particular embodiments described in the present patent application, or to embodiments within the reach of a person skilled in the art. Other embodiments can be envisaged without departing from the scope of the invention, from any element equivalent to an element indicated in the present patent application.

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.

“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited. 

1-19. (canceled)
 20. A heat exchanger, for producing exchanges of heat between a primary liquid and a secondary fluid, the heat exchanger comprising: a plurality of plates disposed parallel to one another; a plurality of spacers extending between the plates and disposed parallel to the other spacers so as to define i) primary channels conformed for the flow of the primary liquid and ii) secondary channels conformed for the flow of the secondary fluid, each primary channel being arranged so as to be able to exchange heat with at least one respective secondary channel; and a primary liquid inlet, configured to be linked fluidically to a primary liquid distributor, wherein each primary channel has an overall prism form with a polygonal section, the prism form being made up of several overall flat faces, and wherein each primary channel comprises rough primary channels, each rough primary channel having microstructure elements having dimensions of between 1 μm and 300 μm, and wherein the microstructure elements are configured such that, for each rough primary channel: r>1+1.3·10³ ·R _(a)·ε in which: r is the ratio of the real surface of a respective rough primary channel, as numerator, to the geometrical surface of a respective rough primary channel, as denominator, R_(a) (in m) is the arithmetic mean deviation relative to the median line, and ε is the void fraction of the real surface of a respective rough primary channel.
 21. The heat exchanger as claimed in claim 20, wherein each polygonal section has dimensions of between 1 mm and 10 mm.
 22. The heat exchanger as claimed in claim 21, wherein each polygonal section has dimensions of between 3 mm and 7 mm, a rectangular polygonal section having, an approximate length equal to 5 mm and an approximate width equal to 1.5 mm
 23. The heat exchanger as claimed in claim 20, wherein microstructure elements are distributed substantially over all the internal periphery of each rough primary channel.
 24. The heat exchanger as claimed in claim 20, wherein, for each respective rough primary channel, the microstructure elements are distributed over at least 80% of the surface of the rough primary channel.
 25. The heat exchanger as claimed in claim 20, wherein the microstructure elements have mutually similar dimensions and mutually similar forms, and in which the microstructure elements are configured such that, for each rough primary channel: r>1+1.3·10³ ·h·ε in which: h (in m) is the mean height of the microstructure elements.
 26. The heat exchanger as claimed in claim 20, wherein the microstructure elements are distributed uniformly.
 27. The heat exchanger as claimed in claim 26, wherein the microstructure elements are configured such that, for each rough primary channel: $d < \sqrt{\frac{7.5 \cdot 10^{- 4} \cdot P}{ɛ}}$ in which: d (in m) is the mean distance between the centers of the adjacent microstructure elements, the centers being situated on the geometrical surface of the rough primary channel, P (in m) is the mean perimeter of the section of the microstructure elements.
 28. The heat exchanger as claimed in claim 27, wherein the microstructure elements are configured such that, for each rough primary channel: $\frac{r - 1 - {1.3 \cdot 10^{3} \cdot h \cdot ɛ}}{{ɛ/h}{6.7 \cdot {10^{- 6}/d^{2}}}} > {4.2 \cdot 10^{- 8}}$ and in which the microstructure elements are also configured such that, for each rough primary channel: $d > \sqrt{\frac{S}{0.4}}$ in which: S (in m²) is the mean surface of the section of the microstructures.
 29. The heat exchanger as claimed in claim 26, wherein the microstructure elements are distributed only on the long sides of the rectangular base.
 30. The heat exchanger as claimed in claim 20, wherein the microstructure elements have irregular forms, the microstructure elements also being able to be distributed non-uniformly.
 31. The heat exchanger as claimed in claim 30, wherein the microstructure elements are configured such that, for each rough primary channel: $\frac{r - 1 - {1.3 \cdot 10^{3} \cdot R_{a} \cdot ɛ}}{{ɛ/R_{a}} + {1.2 \cdot 10^{5}}} > {4.2 \cdot {10^{- 8}.}}$
 32. The heat exchanger as claimed in claim 20, wherein each rough primary channel out of at least a part of the rough primary channels has an overall prism form with rectangular base.
 33. The heat exchanger as claimed in claim 20, wherein the microstructure elements are distributed so as to define between them passages for the flow of the primary liquid.
 34. The heat exchanger as claimed in claim 20, wherein each rough primary channel has an arithmetic roughness Ra of between 1 μm and 60 μm.
 35. The heat exchanger as claimed in claim 20, wherein each rough primary channel has nanostructure elements distributed over at least 80% of its length, each nanostructure element having dimensions of between 1 nm and 500 nm.
 36. The heat exchanger as claimed in claim 20, wherein the microstructure elements are formed by a treatment of the surface of each primary element, wherein the treatment is selected from the group consisting of anodization; sandblasting; shotblasting; chemical etching; powder sintering; molten metal projection; laser; photolithography; mechanical etching of rolling, brushing, or printing type; and combinations thereof.
 37. The heat exchanger as claimed in claim 20, wherein the heat exchanger is configured to form a vaporizer-condenser, the lengths of the rough primary channels and the lengths of the secondary channels being determined such that the exchanges of heat make it possible to totally or partially vaporize the primary liquid and to totally or partially condense the secondary fluid introduced in secondary gas form.
 38. The heat exchanger as claimed in claim 20, wherein said primary liquid inlet is placed at an altitude greater than the rough primary channels when the heat exchanger is in service such that the primary liquid distributor introduces the primary liquid in the form of a film flowing by gravity through said at least one primary liquid inlet into the rough primary channels.
 39. A separation unit, for separating gas by cryogenics, the separation unit comprising at least one vaporizer-condenser-forming heat exchanger as claimed in claim 20, the vaporizer-condenser being configured to allow an exchange of heat between a liquid containing oxygen and a gas containing nitrogen. 